Great work. I my humble opinion I think you should offer the 4k resolution at a price as I'm repinning all of these on Pinterest! One of the spacescapes I repinned(unfortunately it was another one, not yours) has 87 re-pins. I went through and counted up the followers and assuming everyone saw it it's close to 15k views. Even if you cut that in half you're still talking a decent chunk of people. Considering there is little to no wallpaper resources for 4k(to my knowledge) you could totally dominate a niche. Just my two cents.